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    <title>Document</title>
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    <p>不论鼠标指针穿过被选元素或其子元素，都会触发 mouseover 事件。</p>
    <p>只有在鼠标指针穿过被选元素时，才会触发 mouseenter 事件。</p>
    <div class="over" style="background-color:lightgray;padding:20px;width:40%;float:left">
        <h2 style="background-color:white;">被触发的 Mouseover 事件：<span></span></h2>
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    <div class="enter" style="background-color:lightgray;padding:20px;width:40%;float:right">
        <h2 style="background-color:white;">被触发的 Mouseenter 事件：<span></span></h2>
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